DNA (deoxyribonucleic acid) carrying genetic information in living organisms is one of the most important materials for life process. DNA has the capability of extremely precise molecular-recognition, because DNA forms a double-stranded structure between two complementary strands via base pairs between them. Based on this principle, genetic diagnosis that uses the DNA chip has been developed. Application to biosensors and molecular devices is also expected. Also since the DNA double helix allows selective intercalation of an aromatic compound having a planar chemical structure, it is useful in removing a carcinogenic compound and the like, and is expected to be useful as an environmental cleaning material for removing a harmful substance in air or water (see FUNCTION & MATERIALS, Vol. 19, 1999).
For example, DNA chips carrying a lot of DNA fragments (DNA probes) on the surface of a substrate like a slide glass have been developed. Since DNA is naturally water-soluble, DNA must be immobilized onto the substrate for such applications. In order to immobilize a biological substance on a substrate, organic crosslinking reaction is conventionally utilized. For instance, there is a method of supporting a biological substance such as nucleic acid, protein and peptide on the roughened surface of a slide glass having a surface layer of a carbon-based material (see Japanese Patent Application Laid-open No. 2002-211954). In this method, first the carbon surface is carboxylized and subjected to dehydration-polycondensation with carbodiimide and N-hydroxysuccinimide to form active ester groups such as N-hydroxysuccinimide ester group on the end of the hydrocarbons through an amide bond, and then the biological substance to be supported is bonded to the activated surface. Also a method and a kit for quantitatively detecting nucleic acid are disclosed in Japanese Patent Application Laid-open No. H11-148935.
Furthermore, a method for immobilizing nucleic acid on a substrate is disclosed where the substrate is activated by using atomic-oxygen plasma to immobilize nucleic acid thereon (see Japanese Patent Application Laid-open No. 2002-218976). Any one of these technologies has such problems that the supporting region is limited to the surface of the substrate and the process is complicated.
In addition to the organic crosslinking reaction, a crosslinking reaction with a metal ion was also proposed. Japanese Patent Application Laid-open No. H7-41494 discloses a method for immobilizing a deoxyribonucleic acid by coagulating an alkaline metal salt of the deoxyribonucleic acid and an alkaline metal salt of alginic acid using a divalent metal-containing compound.
Meanwhile, concerning the use of DNA as an environmental cleaning material, Japanese Patent Application Laid-open No. 2001-81098 proposes a material where DNA is solidified and immobilized on a support by irradiating UV light of 250 to 270 nm to a liquid film or thin layer of water-soluble DNA on the support. Further, Japanese Patent Application Laid-open No. H10-175994 discloses a DNA complex where DNA is immobilized on an inorganic solid. In these methods DNA is crosslinked to develop water resistance, but there are such problems that the exposed area of DNA is small and functions of DNA are not developed efficiently.
U.S. Pat. No. 6,303,290 discloses a method for immobilizing a biological material on a matrix of silica colloid. In this method, although the matrix has a large number of micropores, the matrix strength is not enough.